Abstract Detail

Symbioses: Plant, Animal, and Microbe Interactions

Kates, Heather [1], Folk, Ryan [2], Guralnick, Robert [3], LaFrance, Raphael [4], O’Meara, Brian [5], Soltis, Douglas [1], Soltis, Pamela [7].

Two shifts in evolutionary lability explain many independent origins of nitrogen-fixing nodulation symbiosis in angiosperms.

Symbiotic nitrogen fixation via root nodulation (SNFN) is a complex trait that requires coordinated control of multiple plant host and bacterial symbiont genes. All flowering plant lineages known to undergo SNFN occur within a single clade of angiosperms sometimes referred to has the ‘Nitrogen-fixing clade’ (NFC). The NFC includes ~8% of all flowering plants (~31,200 species), comprising orders Rosales, Fagales, Cucurbitales, and Fabales. Within this large clade, nodulation is present intermittently with only 10 of 28 families containing species capable of nodulation. Pinpointing the evolutionary origins of SNFN is critical for understanding its genetic basis, but has long been complicated by data limitations and its scattered presence in a single species-rich clade of flowering plants. Here we use the largest purpose-built phylogeny for any lineage (~15,000 species), along with an enhanced trait database, to reconstruct the evolution of SNFN. We show that shifts among heterogeneous evolutionary rates can explain how SNFN could arise many times across a large phylogeny by identifying the evolutionary pathway to SNFN gain. Our analyses suggest a two-step process where an ancestral deep precursor state gives rise to a more labile state from which SNFN was easily gained at certain points in the NFC. Our reconstruction of ancestral states illustrates how this two-step pathway could have led to 16 likely origins of SNFN in the NFC; these gains include six origins of rhizobial SNFN in the legumes and one in Parasponia, and nine origins of actinorhizal associations in the other families with SNFN. In addition to multiple gains, we also infer 10 putative losses. Our findings of recurrent gains agree with earlier broad phylogenetic approaches, but contrast to some current genomic hypotheses invoking a single gain and multiple losses. SNFN may be an example of multi-level convergent evolution, thus requiring a broader phylogenetic and genetic scope when performing genome-phenome mapping to fully elucidate mechanisms enabling SNFN.

1 - University Of Florida, Florida Museum Of Natural History, Dickinson Hall, Gainesville, FL, 32611, United States
2 - Mississippi State University, Biological Sciences, 295 E. Lee Blvd., P.O. Box GY, Mississippi State, MS, 39762, United States
3 - Florida Museum Of Natural History, 358 Dickinson Hall, University O, 358 Dickinson Hall, University Of Florida, Gainesville, FL, 32611, United States
4 - University of Florida, Florida Museum of Natural History, Dickinson Hall, Gainesville, FL, 32611, United States
5 - University of Tennessee, Department of Ecology and Evolutionary Biology, Knoxville, TN, 37996, USA
6 - University Of Florida, Florida Museum Of Natural History, Dickinson Hall, Gainesville, FL, 32611, United States
7 - University Of Florida, Florida Museum Of Natural History, Gainesville, FL, 32611.0, United States

Keywords:
nitrogen-fixing plants
phylogenomics
nodulation
Symbiosis
nitrogen fixation.

Presentation Type: Oral Paper
Number: SYM2005
Abstract ID:826
Candidate for Awards:None